A B757-200 FLC DSNDED BELOW A DC8 XING THE RWY 35L FINAL APCH PATH AT SDF.

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WE ENTERED THE SDF AIRSPACE OVER DARBY INTXN; WHICH IS SE OF SDF. ATIS RPTED LNDG ON RWY 35R&L. WE ADVISED ATC WE WERE PARKING ON RAMP X; WHICH IS CLOSER TO RWY 35L. ATC SAID 'EXPECT RWY 35R.' LATER ADVISED OF VISUAL TO RWY 35L. WE WERE SLOWED TO 210 KTS AT 8000 FT THEN TO DSND TO 4000 FT. LATER CLRED TO INTERCEPT LOC RWY 35L; DSND TO 2500 FT. WHILE ABOVE 4000 FT; GIVEN TFC AT 11 O'CLOCK LEAVING 4500 FT; DSNDING 4000 FT; LNDG RWY 35R; TFC WAS SBOUND; PARALLEL TO US IN OPPOSITE DIRECTION. I CALLED TFC IN SIGHT AND WE WERE TOLD; 'MAINTAIN VISUAL SEPARATION FROM THAT TFC; CLRED FOR THE VISUAL APCH; RWY 35L.' WE WERE SLIGHTLY ABOVE 4000 FT; BUT BELOW THE GS AND HAD BEEN DSNDING AT 210 KTS SINCE LEAVING 8000 FT. AT THIS TIME I OBSERVED THE OTHER AIRPLANE; A DC8; TURNING L TO CROSS OUR FLT PATH ON THE LOC. I TOLD THE FO; WHO WAS FLYING; TO 'HUSTLE DOWN TO 3000 FT.' HE PUSHED THE NOSE DOWN AND INCREASED OUR RATE OF DSCNT; BUT WE WERE BTWN 3200 FT AND 3400 FT WHEN WE PASSED BENEATH THE DC8. I ASKED THE CTLR THE ALT OF THE OTHER ACFT AND HE SAID '4000 FT.' I SAID THAT WAS A LITTLE TOO CLOSE FOR ME AND HE APOLOGIZED AND SAID HE HAD 'TURNED HIM IN TOO SOON.' THIS WAS A CASE OF LACK OF TCASII AND ACFT FROM E LNDG ON W RWY; ACFT FROM W LNDG ON E RWY TO SHORTEN TAXI TIME. WITHOUT TCASII I WAS GUESSING ON THE DC8'S ALT.